The parallel motion device of the present invention is applicable to many situations and structures wherein it is desired to maintain an elongated shiftable member substantially perpendicular to the direction in which it is being shifted. The parallel motion linkage is particularly adapted for use with the sliding keyboard cover of a piano, and for purposes of an exemplary showing will be described in this application.
It has been common practice to provide the sliding keyboard cover of a piano with some form of parallel motion device to assure that the cover will slide straight and will not skew or jam between the sides of the piano case. Numerous parallel motion mechanisms have been employed such as a scissors type device and a cable and pulley device. Since the 1930s, the most usual type of parallel motion device has comprised a torque rod terminating in cranks at each end to transfer motion from one end of the sliding key cover to the other.
The torque rod mechanism works very well when properly built and installed. Nevertheless, it is characterized by certain deficiencies. First of all, it is difficult to accurately locate and attach the crank terminating linkages in the piano case. As a result, pianos equipped with this mechanism can exhibit a variety of malfunctions. The mounting screws for the linkage are often located in nearly inaccessible places, making removal of the cover for piano tuning or servicing in the field very difficult. Removing the sliding keyboard cover often scratches the piano case. The torque rod mechanism offers little or no adjustment. Furthermore, it must be manufactured in some three to five lengths to accommodate the basic types and sizes of pianos.
The parallel motion linkage of the present invention is easily installed. The sliding keyboard cover may be readily and quickly removed and replaced for piano servicing and tuning in the field. The parallel motion linkage taught herein constitutes a simpler and more efficient mechanism than the prior art structures and affords complete and easy adjustment of the forward stopping position and the parallel condition of the sliding keyboard cover. Furthermore, the mechanism is quiet in operation, and with a single change in tie rod length is applicable to substantially any size and model of piano.